A light-emitting diode (LED) is an example of a light-emitting element. An LED is a device that emits light due to electron-hole pairs near a p-n junction or in an active layer by flowing current through a terminal of a compound semiconductor. Recently, advances in semiconductor technologies have led to rapid progress in producing high-quality LEDs. For example, technologies that implement a blue LED with high brightness by forming a III-V group nitride layer on a sapphire substrate using a metal-organic chemical vapor deposition (MOCVD) method are being commercialized.
As described above, a conventional LED has been manufactured by depositing a compound mainly on a sapphire substrate. However, although a sapphire substrate has an excellent light transmission property and mechanical strength, it also has disadvantages such as low thermal conductivity and difficulty in processing. In addition, a laser lift-off process is required to manufacture a vertical type light-emitting diode.
Graphene may be considered as a candidate material for replacing the sapphire substrate. Graphene is a monolayer of carbon atoms which are connected to form a honeycomb-shaped two-dimensional planar structure. An experimental method for obtaining graphene was first reported in 2004 by Ander K. Geim of Manchester University, who mechanically separated graphene from graphite. Since then, physical and chemical characteristics of graphene have been studied, and in recent years, technology for growing graphene on a large substrate having a size of to about 30 inches using chemical vapor deposition (CVD) has emerged. A material having a layered structure with two or more sheets of graphene is graphite. That is, a single layer separated from graphite is graphene.
Graphene has excellent thermal and electrical conductivity, high chemical/mechanical stability, and high transparency. In addition, graphene has high electron mobility, low resistivity, and a large surface area, and has an advantage over carbon nanotubes on a commercial front. Further, graphene or layer-structured graphite including graphene may be easily separated from an original substrate and transferred to another substrate.
In spite of the above-described merits, there have been limits in using graphene in a semiconductor device. In particular, since the surface of graphene is chemically very stable and non-reactive, it is very difficult to grow a microstructure or thin-film on graphene.